1. Field of the Invention
The present invention relates to rotatable cutting tool assemblies and more specifically to rotatable cutting tool assemblies having sleeve retainers for removable attachment of the cutting tool within a bored tool holder.
2. Description of the Related Art
The present invention is directed toward a cutting tool assembly employed in earth working, mining or construction applications wherein a cutting bit is held on a mounting block or bit holder that is affixed to a movable member. Such cutting tool assemblies have been employed for various excavating operations. These excavating operations can include removal of minerals as well as trenching, concrete cutting, road planing and other construction applications. The effective life expectancy of cutting tools is determined by the cutting tool's ability to be securely held in place and yet be free to rotate in order to promote uniform wear on the respective tip portions. While earlier cutting tool assemblies have performed satisfactorily, certain problems or drawbacks have existed, and the subject invention is directed toward overcoming these problems.
There is a need in the art for a cutting tool assembly wherein the cutting bit will be adequately retained within the mounting block for an extended lifetime without inadvertent removal of the cutting bit due to the forces acting thereon during excavating operations.
Prior art cutting tool assemblies have employed cylindrical retainer sleeve clips with cutting tool shanks that have an annular groove closer to the rear portion of the shank for receiving stop tabs that axially fix replaceable cutting tools inside the bore of a bit holder. In U.S. Pat. No. 5,503,463 to Ojanen, a cylindrical retainer has inward stop fingers that are received by the annular groove on the shank and outwardly directed fingers that are received in an annular groove in the bit holder bore sidewall.
In U.S. Pat. No. 4,921,310 to Hedlund and U.S. Pat. No. 4,684,176 to Den Besten prior art designs, the fingers are formed by shear cuts made in the retainer and deflecting the finger stops radially inward. FIGS. 1-3 are representative of such prior art cutting tool assemblies. In these prior art designs the retainers often failed prematurely due to cracks and splits that developed at a shear cut edge at the axially rearward end of stop tab opening. Such stop tab opening shear cut lines locally weakens the retainer's strength and resistance to fracture. As shown at 7 in FIG. 3, cracks/splits in the prior art retainers propagated at these shear cut lines on the retainer's stop tab opening primarily along the axial direction of the retainer or in a direction perpendicular to the axial direction of the retainer. In FIG. 2 the hub 2 of the prior art cutting tool's shank contacts and rotates up against the stop tab openings 4 rearward shear cut line 6 during heavy loads. This contact in prior art designs applies a shearing force that is concentrated along the retainer opening and causes a propagating fracture. German patent application DE 109720635A1 to Moosmann discloses stop fingers 26 and a cooperating groove 27 for axially positioning the cutting tool shank within the bit holder. Such designs are more likely to fracture/crack along the shear cut lines than along the other positions of the retainer.
The fracture of the retainer in the field causes difficulty in removing the retainer from the bit holder. When an operator attempts to remove the retainer for replacement, it occasionally breaks off and additional time and tools are needed to remove the portion of the retainer remaining in the bit holder. In the prior art the cutting tool and a portion of the retainer are dislodged during operation when a reverse load is applied to the cutting tool.
Fractured retainers make used tools difficult to remove or the retainer sticks in the bore and the tool shank is ejected without the retainer. The retainer must then be driven out separately. This creates production delays in changing the tool. A fractured retainer typically takes 5 minutes to change whereas an undamaged retainer can be removed in about 30 seconds. It isn't unusual that it may take 30 minutes to remove a fractured retainer from a support block. A typical change of the set of tools on a have lane construction machine normally takes about 30 minutes. If 2-3 retainers are fractured it can take from anywhere between 15-90 minutes more time. This additional downtime needed to remove fractured retainers increases required labor costs.
Retainer fracture and failure in the prior art is often attributed to relative axial movement between the retainer and cutting tool shank. In U.S. Pat. No. 4,921,310 to Hedlund, retainer stop tabs 12 are received in an annular groove on the cutting tool shank. The amount of axial play of the cutting tool in prior art devices such as the embodiment in FIG. 6 of Hedlund increases during the lifetime of the tool on account of wear occurring to the stop fingers.
The premature wear and fracture of cylindrical retainers on cutting tool assemblies requires the cutting tool assemblies to be more frequently replaced and/or inspected. When the retainer is worn or fractured the shank of the tool oftentimes becomes locked up and stops rotating. Once the tool stops rotating the cutting tool bit becomes unevenly worn on one side and the cutting bit quickly becomes damaged and inoperative. Some cutting bits are knocked out and become lost after the retainer is fractured or worn. Other bits become locked within the bit holder as the worn retainer pieces wedge the shank within the bit holder. Such bit holders on rotary drums must be removed and attached back onto the drum.
The subject invention overcomes the problems in the prior art in a cutting tool assembly having a retainer scheme which effectively and rotatably retains the cutting bit within the mounting block while at the same time preventing premature failure of the cutting bit retainer during excavating operations.